FIG. 6 is a block diagram illustrating the circuit structure of conventional inertial force sensor 100A.
As illustrated in FIG. 6, conventional inertial force sensor 100A is, for example, an angular velocity sensor, and includes oscillator 1, drive circuit 7, detection circuit 8, adder 9, temperature sensor 10, A/D converter 11, and storage 12.
Oscillator 1 is a crystal oscillator in tuning fork form. Drive electrode 2 made of gold is provided on each of the four side surfaces of oscillator 1. Monitor electrode 3 made of gold is provided on each of the front and back surfaces of oscillator 1. GND electrode 4 made of gold is provided on the inner side surface of oscillator 1, and first detection electrode 5 and second detection electrode 6 made of gold are provided on the outer side surface of oscillator 1.
Drive circuit 7 receives the charge of one monitor electrode 3 of oscillator 1 as input, and outputs a drive signal to drive electrode 2 in oscillator 1.
Detection circuit 8 receives the charge generated by the Coriolis force in first detection electrode 5 and the charge generated by the Coriolis force in second detection electrode 6 in oscillator 1 as input, and outputs an angular velocity signal as an output signal.
Adder 9 adds a correction signal to the angular velocity signal output from detection circuit 8.
Temperature sensor 10 is located near oscillator 1, and detects the temperature near oscillator 1.
A/D converter 11 converts an analog signal output from temperature sensor 10 into a digital signal.
Storage 12 is memory such as EEPROM. Storage 12 stores correction data for correcting the error of the output signal output from detection circuit 8.
The following describes the operation of conventional inertial force sensor 100A having the aforementioned structure.
When an alternating-current (AC) voltage is applied to drive electrode 2 in oscillator 1, oscillator 1 resonates, and a charge is generated in monitor electrode 3 in oscillator 1. The charge generated in monitor electrode 3 is fed to drive electrode 2 via drive circuit 7, and the oscillation of oscillator 1 is adjusted to a constant amplitude.
When oscillator 1 rotates at angular velocity ω about the longitudinal central axis of oscillator 1 in a state where oscillator 1 is bending-oscillating at velocity v in the oscillation direction, the Coriolis force of F=2 mV×ω is generated in oscillator 1. This Coriolis force causes the generation of a charge in first detection electrode 5 and second detection electrode 6. The charge generated in first detection electrode 5 and second detection electrode 6 is fed to detection circuit 8, and an angular velocity signal is output from detection circuit 8 as an output signal.
Consider the case where inertial force sensor 100A (angular velocity sensor) is installed in an engine room in a vehicle and the temperature near inertial force sensor 100A changes from −40° C. to 100° C.
First, the temperature near inertial force sensor 100A is changed from −40° C. to 100° C. so that the conditions are the same as those in the engine room in the vehicle, and the output signal from temperature sensor 10 at each temperature is fed to CPU 14 via A/D converter 11 and at the same time the output signal from detection circuit 8 in a state where no angular velocity is provided is fed to CPU 14. CPU 14 plots the output signal at each temperature so that the output signal of detection circuit 8 at each temperature (for example, every 1° C.) is always 2.5 V which is zero output, to obtain a correction curve. CPU 14 then approximates the correction curve by a quadratic curve (quadratic function) as illustrated in FIG. 7, to calculate correction coefficients. The correction coefficients are, for example, a=7×10−6, b=9×10−4, and c=2.5, and stored in storage 12 together with the correction curve as correction data.
In the case where angular velocity is applied to the vehicle (not illustrated) provided with inertial force sensor 100A set in this way, detection circuit 8 in inertial force sensor 100A outputs an angular velocity signal.
In this case, CPU 14 in vehicle control device 13 in the vehicle calculates a correction signal (correction value) based on the correction data stored in storage 12 in inertial force sensor 100A, and D/A converter 15 converts the calculated correction signal into an analog signal. Adder 9 adds the analog correction signal to the angular velocity signal output from detection circuit 8. The output signal from detection circuit 8, that is, the angular velocity signal, is corrected in this way.
For example, Patent Literature (PTL) 1 is known as related art document information for the invention of this application.